Pressure container with differential vacuum panels

ABSTRACT

A plastic container (1) has a first set of flex panels (2) and a second set of flex panels (3) one set being adapted to react to pressure changes within the container to a different degree than the other set. This can be achieved by different curvature and/or size and/or different distance from a central longitudinal axis of the container. At least one of the panels has at least two different extents of curvature. In some embodiments one or more of the panels may be flat.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 12/595,830, filed Oct. 13, 2009 (the '830application), currently pending and published as US2010/0116778, whichis the U.S. National Phase of International Application No.PCT/NZ2008/000079, filed Apr. 11, 2008, and published as WO08/127130 onOct. 23, 2008, which claims priority to New Zealand Application No.554532, filed Apr. 13, 2007.

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 13/270,886, filed Oct. 11, 2011 (the '886application), currently pending, which is a continuation of U.S. patentapplication Ser. No. 11/664,265, filed Jun. 16, 2008, now U.S. Pat. No.8,186,528, issued May 29, 2012, which is the U.S. National Phase ofInternational Application No. PCT/US2005/035241, filed Sep. 30, 2005,and published as WO06/039523 on Apr. 13, 2006, which claims priority toNew Zealand Application No. 535772, filed Sep. 30, 2004.

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 13/357,232, filed Jan. 24, 2012, currently pending,which is a divisional of U.S. patent application Ser. No. 11/664,265,filed Jun. 16, 2008, now U.S. Pat. No. 8,186,528, issued May 29, 2012,which is the U.S. National Phase of International Application No.PCT/US2005/035241, filed Sep. 30, 2005, which claims priority to NewZealand Application No. 535772, filed Sep. 30, 2004.

The disclosures, publications and patents of each of the aforementionedapplications are incorporated herein by reference thereto.

FIELD OF THE INVENTIONS

The present invention relates to hot-fillable containers. Moreparticularly, the present invention relates to hot-fillable containershaving collapse panels.

BACKGROUND OF THE INVENTIONS

‘Hot-Fill’ applications impose significant and complex mechanical stresson a container structure due to thermal stress, hydraulic pressure uponfilling and immediately after capping, and vacuum pressure as the fluidcools.

Thermal stress is applied to the walls of the container uponintroduction of hot fluid. The hot fluid will cause the container wallsto soften and then shrink unevenly, causing distortion of the container.The polyester must therefore be heat-treated to induce molecular changesresulting in a container that exhibits thermal stability.

Pressure and stress act upon the side walls of a heat resistantcontainer during the filling process, and for a significant period oftime thereafter. When the container is filled with hot liquid andsealed, there is an initial hydraulic pressure and an increased internalpressure is placed upon containers. As the liquid, and the air headspaceunder the cap, subsequently cool, thermal contraction results in partialevacuation of the container. The vacuum created by this cooling tends tomechanically deform the container walls.

Generally speaking, containers incorporating a plurality of longitudinalflat surfaces accommodate vacuum force more readily. Agrawal et al, U.S.Pat. No. 4,497,855 discloses a container with a plurality of recessedcollapse panels, separated by land areas, which allows uniformly inwarddeformation under vacuum force. The vacuum effects are controlledwithout adversely affecting the appearance of the container. The panelsare drawn inwardly to vent the internal vacuum and so prevent excessforce being applied to the container structure, which would otherwisedeform the inflexible post or land area structures. The amount of ‘flex’available in each panel is limited, however, and as the limit isapproached there is an increased amount of force that is transferred tothe side walls.

To minimise the effect of force being transferred to the side walls,much prior art has focused on providing stiffened regions to thecontainer, including the panels, to prevent the structure yielding tothe vacuum force.

The provision of horizontal or vertical annular sections, or ‘ribs’,throughout a container has become common practice in containerconstruction, and is not only restricted to hot-fill containers. Suchannular sections will strengthen the part they are deployed upon.Cochran U.S. Pat. No. 4,372,455 discloses annular rib strengthening in alongitudinal direction, placed in the areas between the flat surfacesthat are subjected to inwardly deforming hydrostatic forces under vacuumforce. Akiho Ota et al U.S. Pat. No. 4,805,788 discloses longitudinallyextending ribs alongside the panels to add stiffening to the container.Akiho Ota also discloses the strengthening effect of providing a largerstep in the sides of the land areas. This provides greater dimension andstrength to the rib areas between the panels. Akiho Ota et al, U.S. Pat.No. 5,178,290 discloses indentations to strengthen the panel areasthemselves.

Akiho Ota et al, U.S. Pat. No. 5,238,129 discloses further annular ribstrengthening, this time horizontally directed in strips above andbelow, and outside, the hot-fill panel section of the bottle.

In addition to the need for strengthening a container against boththermal and vacuum stress, there is a need to allow for an initialhydraulic pressure and increased internal pressure that is placed upon acontainer when hot liquid is introduced followed by capping. This causesstress to be placed on the container side wall. There is a forcedoutward movement of the heat panels, which can result in a barreling ofthe container.

Thus, Hayashi et al, U.S. Pat. No. 4,877,141, discloses a panelconfiguration that accommodates an initial, and natural, outward flexingcaused by internal hydraulic pressure and temperature, followed byinward flexing caused by the vacuum formation during cooling.Importantly, the panel is kept relatively flat in profile, but with acentral portion displaced slightly to add strength to the panel butwithout preventing its radial movement in and out. With the panel beinggenerally flat, however, the amount of movement is limited in bothdirections. By necessity, panel ribs are not included for extraresilience, as this would prohibit outward and inward return movement ofthe panel as a whole.

As stated, the use of blow molded plastic containers for packaging“hot-fill” beverages is well known. However, a container that is usedfor hot-fill applications is subject to additional mechanical stresseson the container that result in the container being more likely to failduring storage or handling. For example, it has been found that the thinsidewalls of the container deform or collapse as the container is beingfilled with hot fluids. In addition, the rigidity of the containerdecreases immediately after the hot-fill liquid is introduced into thecontainer. As the liquid cools, the liquid shrinks in volume which, inturn, produces a negative pressure or vacuum in the container. Thecontainer must be able to withstand such changes in pressure withoutfailure.

Hot-fill containers typically comprise substantially rectangular vacuumpanels that are designed to collapse inwardly after the container hasbeen filled with hot liquid. However, the inward flexing of the panelscaused by the hot-fill vacuum creates high stress points at the top andbottom edges of the vacuum panels, especially at the upper and lowercorners of the panels. These stress points weaken the portions of thesidewall near the edges of the panels, allowing the sidewall to collapseinwardly during handling of the container or when containers are stackedtogether. See U.S. Pat. No. 5,337,909.

The presence of annular reinforcement ribs that extend continuouslyaround the circumference of the container sidewall are shown in U.S.Pat. No. 5,337,909. These ribs are indicated as supporting the vacuumpanels at their upper and lower edges. This holds the edges fixed, whilepermitting the center portions of the vacuum panels to flex inwardlywhile the bottle is being filled. These ribs also resist the deformationof the vacuum panels. The reinforcement ribs can merge with the edges ofthe vacuum panels at the edge of the label upper and lower mountingpanels.

Another hot-fill container having reinforcement ribs is disclosed in WO97/34808. The container comprises a label mounting area having an upperand lower series of peripherally spaced, short, horizontal ribsseparated endwise by label mount areas. It is stated that each upper andlower rib is located within the label mount section and is centeredabove or below, respectively, one of the lands. The container furthercomprises several rectangular vacuum panels that also experience highstress point at the corners of the collapse panels. These ribs stiffenthe container adjacent lower corners of the collapse panels.

Stretch blow molded containers such as hot-filled PET juice or sportdrink containers, must be able to maintain their function, shape andlabelability on cool down to room temperature or refrigeration. In thecase of non-round containers, this is more challenging due to the factthat the level of orientation and, therefore, crystallinity isinherently lower in the front and back than on the narrower sides. Sincethe front and back are normally where vacuum panels are located, theseareas must be made thicker to compensate for their relatively lowerstrength.

In discussing the above prior art the applicant does not acknowledgethat it forms part of common general knowledge in New Zealand or in anyother country or region.

SUMMARY OF THE INVENTIONS

The present invention provides according to one aspect a plasticcontainer, having a body portion including a sidewall, wherein said bodyportion includes; a first controlled deflection flex panel on onesidewall portion and a second controlled deflection flex panel on asecond sidewall portion, at least one of said controlled deflection flexpanels having at least two different extents of outward curvature, saidfirst and second flex panels being adapted to react to pressure changeswithin the container to a different degree. By way of example, acontainer having four controlled deflection flex panels may be disposedin two pairs on symmetrically opposing sidewalls, whereby one pair ofcontrolled deflection flex panels responds to vacuum force at adifferent rate to an alternately positioned pair. The pairs ofcontrolled deflection flex panels may be positioned an equidistance fromthe central longitudinal axis of the container, or may be positioned atdiffering distances from the centerline of the container. In additionthe design allows for a more controlled overall response to vacuumpressure and improved dent resistance and resistance to torsiondisplacement of post or land areas between the panels. Further, improvedreduction in container weight is achieved, along with potential fordevelopment of squeezable container designs.

According to another aspect of the invention a container foraccommodating volume contraction within the container after being filledwith a heated liquid has a side wall portion having four flex panelsspaced apart around the circumference of a body portion and arranged asa first pair of opposed panels and a second pair of opposed panels, atleast one of said flex panels having at least two different extents ofcurvature wherein the panels can deform inwardly to accommodate vacuumpressure caused by volume contraction of the heated liquid and whereinthe panels are formed so the first pair of panels deforms inwardly at adifferent rate than the second pair of panels. Preferably each flexpanel may have a generally variable outward curvature with respect tothe centerline of the container. The first pair of panels may bepositioned whereby one panel in the first pair is disposed opposite theother, and the first pair of panels has a geometry and surface area thatis distinct from the alternately positioned second pair of panels. Thesecond pair of panels may be similarly positioned whereby the panels inthe second pair are disposed in opposition to each other. The containersare suitable for a variety of uses including hot-fill applications.

In hot-fill applications, the plastic container is filled with a liquidthat is above room temperature and then sealed so that the cooling ofthe liquid creates a reduced volume in the container. In this preferredembodiment, the first pair of opposing controlled deflection flexpanels, having the least total surface area between them, have agenerally rectangular shape, wider at the base than at the top. Thesepanels may be symmetrical to each other in size and shape. Thesecontrolled deflection flex panels have a substantially outwardly curved,transverse profile and an initiator portion toward the central regionthat is less outwardly curved than in the upper and lower regions.Alternatively, the amount of outward curvature could vary evenly fromtop to bottom, bottom to top, or any other suitable arrangement.Alternatively, the entire panel may have a relatively even outwardcurvature but vary in extent of transverse circumferential amount, suchthat one portion of the panel begins deflection inwardly before anotherportion of the panel. Alternatively, one pair of panels may besubstantially flat or concave while the opposing pair of panels comprisecontrolled deflection flex panels having a variable outward curvature.Alternatively again, one pair of panels may be substantially evenlyoutwardly curved, while the opposing pair of panels comprise controlleddeflection flex panels having a variable outward curvature. This firstpair of controlled deflection flex panels may in addition contain one ormore ribs located above or below the panels. These optional ribs mayalso be symmetric to ribs, in size, shape and number to ribs on theopposing sidewalls containing the second set of controlled deflectionflex panels. The ribs on the second set of controlled deflection flexpanels may have a rounded edge which may point inward or outwardrelative to the interior of the container. In a first preferred form ofthe invention, whereby the first pair of controlled deflection flexpanels is preferentially reactive to vacuum forces to a much greaterextent initially than the second pair of controlled deflection flexpanels, it is preferred to not have ribs incorporated within the firstpair of panels, in order to allow easier movement of the panels.

The vacuum panels should be selected so that they are highly efficient.See, for example, PCT application NO. PCT/NZ00/00019 (David Melrose)where panels with vacuum panel geometry are shown. ‘Prior art’ vacuumpanels are generally flat or concave. The controlled deflection flexpanel of Melrose of PCT/NZ00/00019 and the present invention isoutwardly curved and can extract greater amounts of pressure. Each flexpanel has at least 2 regions of differing outward curvature. The regionthat is less outwardly curved, the initiator region, reacts to changingpressure at a lower threshold than the region that is more outwardlycurved. By providing an initiator portion, the control portion (theregion that is more outwardly curved) reacts to pressure more readilythan would normally happen. Vacuum pressure is thus reduced to a greaterdegree than prior art causing less stress to be applied to the containersidewalls. This increased venting of vacuum pressure allows for manydesign options: different panel shapes, especially outward curves;lighter weight containers; less failure under load; less panel areaneeded; different shape container bodies.

The controlled deflection flex panel can be shaped in many differentways and can be used on inventive structures that are not standard andcan yield improved structures in a container.

All sidewalls containing the controlled deflection flex panels may haveone or more ribs located within them. The ribs can have either an outeror inner edge relative to the inside of the container. These ribs mayoccur as a series of parallel ribs. These ribs are parallel to eachother and the base. The number of ribs within the series can be eitheran odd or even. The number, size and shape of ribs are symmetric tothose in the opposing sidewall. Such symmetry enhances stability of thecontainer.

Preferably, the ribs on the side containing the second pair ofcontrolled deflection panels and having the largest surface area ofpanel, are substantially identical to each other in size and shape. Theindividual ribs can extend across the length or width of the container.The actual length, width and depth of the rib may vary depending oncontainer use, plastic material employed and the demands of themanufacturing process. Each rib is spaced apart relative to the othersto optimize its and the overall stabilization function as an inward oroutward rib. The ribs are parallel to one another and preferably, alsoto the container base.

The advanced highly efficient design of the controlled deflection panelsof the first pair of panels more than compensates for the fact that theyoffer less surface area than the larger front and back panels. Byproviding for the first pair of panels to respond to lower thresholds ofpressure, these panels may begin the function of vacuum compensationbefore the second larger panel set, despite being positioned furtherfrom the centerline. The second larger panel set may be constructed tomove only minimally, and relatively evenly in response to vacuumpressure, as even a small movement of these panels provides adequatevacuum compensation due to the increased surface area. The first set ofcontrolled deflection flex panels may be constructed to invert andprovide much of the vacuum compensation required by the package in orderto prevent the larger set of panels from entering an inverted position.Employment of a thin walled super light weight preform ensures that ahigh level of orientation and crystallinity are imparted to the entirepackage. This increased level of strength together with the ribstructure and highly efficient vacuum panels provide the container withthe ability to maintain function and shape on cool down, while at thesame time utilizing minimum gram weight.

The arrangement of ribs and vacuum panels on adjacent sides within thearea defined by upper and lower container bumpers allows the package tobe further light weighted without loss of structural strength. The ribsare placed on the larger, non-inverting panels and the smaller invertingpanels may be generally free of rib indentations and so are moresuitable for embossing or debossing of Brand logos or name. Thisconfiguration optimizes geometric orientation of squeeze bottlearrangements, whereby the sides of the container are partially drawninwardly as the main larger panels contract toward each other. Generallyspeaking, in prior art as the front and back panels are drawn inwardlyunder vacuum the sides are forced outwardly. In the present inventionthe side panels invert toward the centre and maintain this positionwithout being forced outwardly beyond the post structures between thepanels. Further, this configuration of ribs and vacuum panel representsa departure from tradition.

These and various other advantages and features of novelty whichcharacterize the invention are pointed out with particularity in theclaims annexed hereto and forming a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to the accompanying descriptive matter, inwhich there are illustrated and described preferred embodiments of theinvention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of the container showing the embodiment havinga series of symmetrical ribs on the larger controlled deflection flexpanels.

FIG. 2 shows a front view of the container shown in FIG. 1.

FIGS. 3a-c show rendered side, front, and perspective solid views of thecontainer shown in FIGS. 1 and 2.

FIG. 4a shows a Finite Element Analysis view of the container shown inFIG. 1 under vacuum pressure Step One.

FIG. 4b shows a Finite Element Analysis view of the container shown inFIG. 2 under vacuum pressure Step One.

FIG. 5a shows a Finite Element Analysis view of the container shown inFIG. 1 under vacuum pressure Step Two.

FIG. 5b shows a Finite Element Analysis view of the container shown inFIG. 2 under vacuum pressure Step Two.

FIGS. 6a-e show Finite Element Analysis cross-sectional views throughline B-B of the container shown in FIG. 1 under vacuum pressure Step Oneto Five.

FIGS. 7 a-e show front, side and cross-section views of an alternativeembodiment of the container having 2 sets of panels having variablecurvatures.

FIGS. 8 a-e show front, side and cross-section views of an alternativeembodiment of the container having 2 sets of panels having variableprojecting curvatures.

FIGS. 9 a-e show front, side and cross-section views of an alternativeembodiment of the container having 2 sets of panels having variablecurvatures.

FIGS. 10 a-e show front, side and cross-section views of an alternativeembodiment of the container having 2 sets of panels with one set havingan even outward curvature and one set having a variable outwardcurvature.

FIGS. 11 a-e show front, side and cross-section views of an alternativeembodiment of the container having 2 sets of panels with one set ofpanels having variable outward curvatures and one set beingsubstantially flat.

FIGS. 12 a-e show front, side and cross-section views of an alternativeembodiment of the container having 2 sets of panels with one set ofpanels having variable projecting curvatures and one set beingsubstantially flat.

FIGS. 13 a-e show front, side and cross-section views of an alternativeembodiment of the container having 2 sets of panels with one set ofpanels having variable outward curvatures and one set of panels beingsubstantially concave.

FIGS. 14 a-e show front, side and cross-section views of an alternativeembodiment of the container having 2 sets of panels with one set ofpanels having even outward curvatures and one set of panels havingvariable inward curvatures.

DETAILED DESCRIPTION OF THE INVENTIONS

A thin-walled container in accordance with the present invention isintended to be filled with a liquid at a temperature above roomtemperature. According to the invention, a container may be formed froma plastic material such as polyethylene terephthalate (PET) orpolyester. Preferably, the container is blow molded. The container canbe filled by automated, high speed, hot-fill equipment known in the art.

Referring now to the drawings, a preferred embodiment of the containerof this invention is indicated generally in FIG. 1, as generally havingmany of the well known features of hot-fill bottles. The container (1),which is generally round or oval in shape, has a longitudinal axis (C)when the container is standing upright on its base. The containercomprises a threaded neck (5) for filling and dispensing fluid. Neck (5)also is sealable with a cap (not shown). The preferred container furthercomprises a substantially circular base (8) and a bell (4) located belowneck (5) and above base (8). The container of the present invention alsohas a body (9) defined by substantially round sides containing a pair ofnarrower controlled deflection flex panels (2) and a pair of widercontrolled deflection flex panels (3) that connect bell (4) and base(8). A label or labels can easily be applied to the bell area usingmethods that are well known to those skilled in the art, includingshrink wrap labeling and adhesive methods. As applied, the label extendseither around the entire bell of the container or extends over a portionof the label mounting area.

Generally, the substantially rectangular flex panels (3) containing oneor more ribs (6) are those with a width greater than the pair of flexpanels adjacent (2) in the body area (9). The placement of thecontrolled deflection flex panel (3) and the ribs (6) are such that theopposing sides are symmetrical. These flex panels (3) have roundededges. The vacuum panels (3) permit the bottle to flex inwardly uponfilling with the hot fluid, sealing, and subsequent cooling. The ribs(6) can have a rounded outer or inner edge, relative to the spacedefined by the sides of the container. The ribs typically extend most ofthe width of the side and are parallel with each other and the base. Thewidth of these ribs is selected consistent with achieving the ribfunction. The number of ribs on either adjacent side can vary dependingon container size, rib number, plastic composition, bottle fillingconditions and expected contents. The placement of ribs on a side canalso vary so long as the desired goal(s) associated with theinterfunctioning of the ribbed flex panels and the non-ribbed flexpanels is not lost. The ribs are also spaced apart from the upper andlower edges of the vacuum panels, respectively, and are placed tomaximize their function. The ribs of each series are noncontinuous,i.e., they do not touch each other. Nor do they touch a panel edge.

The number of vacuum panels is variable. However, two symmetricalpanels, each on the opposite sides of the container, are preferred. Thecontrolled deflection flex panel (3) is substantially rectangular inshape and has a rounded upper edge (10) and a rounded lower edge (11).

As shown in FIG. 1, the narrower side contains the controlled deflectionflex panel (2) that does not have rib strengthening. Of course, thepanel (2) may also incorporate a number of ribs of varying length andconfiguration. It is also preferred that any ribs positioned on thisside correspond in positioning and size to their counterparts on theopposite side of the container.

Each controlled deflection flex panel (2) is generally outwardly curvedin cross-section. Further, the amount of outward curvature varies alongthe longitudinal length of the flex panel, such that response to vacuumpressure varies in different regions of the flex panel. FIG. 6a showsthe outward curvature in cross-section through Line B-B of FIG. 1. Across-section higher through the flex panel region, i.e. closer to thebell, would reveal the outward curvature to be less than through LineB-B, and a cross-section through the flex panel relatively low on thebody and closer to the junction with the base of the container wouldreveal a greater outward curvature than through Line B-B.

Each controlled deflection flex panel (3) is also generally outwardlycurved in cross-section. Similarly, the amount of outward curvaturevaries along the longitudinal length of the flex panel, such thatresponse to vacuum pressure varies in different regions of the flexpanel. FIG. 6a shows the outward curvature in cross-section through LineB-B of FIG. 1. A cross-section higher through the flex panel region,i.e. closer to the bell, would reveal the outward curvature to be lessthan through Line B-B, and a cross-section through the flex panelrelatively low on the body and closer to the junction with the base ofthe container would reveal a greater outward curvature than through LineB-B.

Importantly, the amount of arc curvature contained within controlleddeflection flex panel (2) is different to that contained withincontrolled deflection flex panel (3). This provides greater control overthe movement of the larger flex panels (3) than would be the case if thepanels (2) were not present or replaced by strengthened regions, or landareas or posts for example. By separating a pair of flex panels (3),which are disposed opposite each other, by a pair of flex panels (2),the amount of vacuum force generated against flex panels (3) duringproduct contraction can be manipulated. In this way undue distortion ofthe major panels may be avoided.

In this preferred embodiment, the flex panels 2 provide for earlierresponse to vacuum pressure, thus removing pressure response necessityfrom flex panels 3. FIGS. 6a to 6e show gradual increases in vacuumpressure within the container. Flex panels (2) respond earlier and moreaggressively than flex panels (3), despite the larger size of flexpanels (3) which would normally provide most of the vacuum compensationwithin the container. Controlled deflection flex panels (2) invert andremain inverted as vacuum pressure increases. This results in fullvacuum accommodation being achieved well before full potential isrealized from the larger flex panels (3). Controlled deflection flexpanels (3) may continue to be drawn inwardly should increased vacuum beexperienced under aggressive conditions, such as greatly decreasedtemperature (deep refrigeration) or if the product is aged leading toincreased migration of oxygen and other gases through the plasticsidewalls, also causing increased vacuum force.

The improved arrangement of the present invention provides for a greaterpotential for response to vacuum pressure than prior art. The containermay be squeezed to expel contents as the larger panels (3) are squeezedtoward each other, or even if the smaller panels (2) are squeezed towardeach other. Release of squeeze pressure results in the containerimmediately returning to its intended shape rather than remain buckledor distorted. This is a result of having the opposing set of panelshaving a different response to vacuum pressure levels. In this way, oneset of panels will always set the configuration for the container as awhole and not allow any redistribution of panel set that might normallyoccur otherwise.

Vacuum response is spread circumferentially throughout the container,but allows for efficient contraction of the sidewalls such that eachpair of panels may be drawn toward each other without undue force beingapplied to the posts (7) separating each panel. This overall setup leadsto less container distortion at all levels of vacuum pressure than priorart, and less sideways distortion as the larger panels are broughttogether. Further, a higher level of vacuum compensation is obtainedthrough the employment of smaller vacuum panels set between the largerones, than would otherwise be obtained by the larger ones alone. Withoutthe smaller panels undue force would be applied to the posts by thecontracting larger panels, which would take a less favourableorientation at higher vacuum levels.

The above is offered by way of example only, and the size, shape, andnumber of the panels (2) and the size, shape, and number of the panels(3), and the size, shape, and number of reinforcement ribs is related tothe functional requirements of the size of the container, and could beincreased or decreased from the values given.

FIGS. 7 a-e, show front, side and cross-section views of an alternativeembodiment of the container having 2 sets of panels, the primary panels(2) having variable curvatures whereby their middle portion isrelatively flat, or has a lesser amount of curvature than the portionsin the upper or lower regions of the panel. The secondary panels (3)also have variable curvatures whereby the middle portion has a greateramount of curvature than the regions above and below. This middle regionalso projects outwardly to a lesser extent or degree than the region ofthe panel above or below. By providing a central portion having agreater amount of curvature, or a lesser radius of curvature, thecentral portion is somewhat strengthened against flexure compared to theregions having lesser amounts of curvature, or a greater radius ofcurvature.

By providing such variable curvatures within a panel, a great degree ofcontrol can be exhibited over the panel and how flexure occurs undervacuum pressure. A certain rate of flexure can be obtained with a highdegree of accuracy.

Additionally, by providing for the secondary panel to have a lesserprojecting region in the middle portion, the amount of resistanceintroduced already by the increased amount of curvature can be furthermodified. The lesser projection causes a degree of lesser resistance tovacuum pressure and ensures the central portion flexes at the correctrate.

The primary panels (2) have a lesser outwardly projecting portion in thecentre, and this region also has a lesser amount of curve, or largerradius of curvature than the regions above and below. Therefore, thecombined effect is to control the overall flexure of the four panelsunder vacuum pressure, such that the primary panels flex readily despitehaving a smaller surface area and being further displaced from thecenterline than the secondary panels.

Importantly, the rate of flexure can be controlled between the 2 sets ofpanels to create a better balance and allowing the container to avoiduncontrolled collapse, and to provide for greater vacuum absorption.

As shown in FIGS. 8 a-e, 2 sets of panels having variable projectingcurvatures whereby the primary panels (2) have a similar construction tothe primary panels in FIGS. 7 a-e, but the secondary panels areconstructed to respond at a slightly lower vacuum threshold than thesecondary panels in FIGS. 7 a-e. This is achieved by having thesecondary panels in this instance have the same radius of curvaturethrough the middle portion rather than the smaller radius of curvaturein FIGS. 7 a-e.

FIGS. 9 a-e show an alternative embodiment of the container again,having 2 sets of panels having variable curvatures. In this example thesecondary panels (3) have a middle region that is further weakenedagainst vacuum pressure by having a lesser amount of arc, or increasedradius of curvature, than the regions above or below. Thus, the fourpanels are constructed in a similar manner to those in FIGS. 8 a-e, butthe secondary panels will respond to vacuum pressures earlier bycomparison.

FIGS. 10 a-e show an alternative embodiment of the container having 2sets of panels with one set having an even outward curvature and one sethaving a variable outward curvature. By comparison to the previousexample in FIGS. 9 a-e, the secondary panels (3) are somewhat moreresistant to vacuum pressure as the middle portion shares a commonradius of curvature, and a common projection with the regions above andbeyond. This creates a panel that is stiffer and slower to respond tovacuum pressure. Subsequently, the primary panels (2) respondsignificantly faster than the secondary panels, but overall responsewithin the container is different to all the previous examples.

FIGS. 11 a-e show a further alternative embodiment of the containerhaving 2 sets of panels with one set of panels (3) having variableoutward curvatures and one set of panels (2) being substantially flat.In this example the primary panels (2) will not have the same totalvolume extraction available as in the previous examples and will respondinitially at a similar rate, but then slow in extraction and cause thesecondary panels to in fact speed up in response to vacuum after theinitial volume compensation is achieved.

FIGS. 12 a-e show another alternative embodiment of the container having2 sets of panels with one set of panels having variable projectingcurvatures and one set being substantially flat. Again, the combinationprovides for alternative speed responses between the panels.

FIGS. 13 a-e show front, side and cross-section views of an alternativeembodiment of the container having 2 sets of panels with one set ofpanels having variable outward curvatures and one set of panels beingsubstantially concave. In this embodiment, the primary panels reactearlier to vacuum pressure due to being concave, particularly in themiddle regions, but overall extraction from the primary panels islimited due to the lack of any outward curvature. This causes thesecondary panels (3) to need to provide for a greater amount of theextraction required, whereby the panels are drawn closer to thecenterline and therefore closer together, under vacuum pressure.

FIGS. 14 a-e show an alternative embodiment of the container having 2sets of panels with one set of panels having even outward curvatures andone set of panels having variable inward curvatures. The primary panels(2) are particularly predisposed to reacting in the initial stages inthis embodiment. The concavity is more pronounced in the middle portion,wherein the inward radius of curvature is smaller, such that this regionreacts more quickly. The secondary panels are further configured toencourage this as they are more stiffly constructed, having a more evenoutward curvature. Thus, the secondary panels resist the early vacuumpressures at the same time the primary panels more readily respond tovacuum. This creates a greater difference in response at early stages ofvacuum pressure between the panels.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

All references cited in this specification are hereby incorporated byreference. The discussion of the references herein is intended merely tosummarize the assertions made by their authors and no admission is madethat any reference constitutes prior art relevant to patentability andthe applicant reserves the right to challenge the accuracy andpertinency of the cited references.

Although this invention has been described by way of example and withreference to possible embodiments thereof, it is to be understood thatmodifications or improvements may be made thereto without departing fromthe scope of the invention as defined in the appended claims.

1. A container for accommodating volume contraction within the containerafter being filled with a heated liquid, having a sidewall portionincluding four flex panels spaced apart around the circumference of abody portion, and arranged as a first pair of opposed panels and asecond pair of opposed panels, at least one of said flex panels havingat least two different extents of curvature wherein the panels candeform inwardly to accommodate vacuum pressure caused by volumecontraction of the heated liquid and wherein the panels are formed sothe first pair of panels deforms inwardly at a different rate than thesecond pair of panels.
 2. The container of claim 1 wherein one said pairof panels has a different amount of outward curvature to the other saidpair of panels.
 3. The container of claim 1 wherein one said pair ofpanels is substantially flat.
 4. The container of claim 1 wherein onesaid pair of panels is substantially concave.
 5. The container of claim1 wherein one said pair of panels has a variable outward curvature. 6.The container of claim 1 wherein one said pair of panels has a generallyeven outward radius of curvature, excluding any ribs or grip features onsaid panels.
 7. The container of claim 6 wherein one said pair of panelshas a variable outward projection.
 8. The container of claim 7 wherein asubstantially central section of said panels projects outward to agreater extent.
 9. The container of claim 7 wherein a substantiallycentral section of said panels projects outward to a lesser extent. 10.A container substantially as herein described with reference to any ofthe embodiments of the invention and as shown in any one or more of theaccompanying drawings.
 11. The container of claim 1 wherein said atleast two different extents of curvature comprise varying amounts ofprojection from a plane defined by a longitudinal axis of said at leastone panel.
 12. The container of claim 11 wherein a substantiallyconstant arc of curvature is provided along said longitudinal axis ofsaid at least one panel.
 13. The container of claim 11 wherein avariable arc of curvature is provided along said longitudinal axis ofsaid at least one panel.